Winter deep-sky challenges

Posted by David Eicher
on Saturday, January 13, 2007

The next time you're out observing and you find yourself checking out the same objects one too many times, consider branching out into some new territory. Find a level of object that pushes your equipment and your observational skill, and draw up a list of new things to see. Try sketching the objects carefully with a pad of paper, a dim red flashlight, and a soft pencil (an Eberhard Faber Ebony pencil works best for smudging the faint light of nebulae and galaxies). Many years ago, an old observing buddy, Phil Harrington, cooked up the following list of challenges. I'd like to bring these objects to your attention again, in case you might not be an old-timer who read Phil's articles years ago.

As suggestions go, try the following: With binoculars, see if you can spot M78, the reflection nebula in Orion. This little gem glows at about magnitude 8 and lies 4° east of Mintaka (Delta [δ] Orionis), the westernmost star in Orion's belt. Discovered in 1779 by Pierre Méchain, M78 appears as an oval, gray-green smear of light. The nebula appears slightly brighter on its southern end. The object has a relatively low surface brightness; that is, its light is spread out, making it a challenging target for binoculars.

In a 2-inch or 3-inch scope, try spotting the reflection nebula NGC 1990 in Orion. This faint cloud of light, consisting of starlight bouncing off tiny, dark particles, surrounds the bright star Alnilam (Epsilon [ε] Orionis), the middle star in Orion's "belt." The difficult challenge here is to see the faint nebulosity surrounding the brilliance of the magnitude 1.7 star. A dark, transparent night, squeaky-clean optics, and slow movement of the eyepiece field may help to reveal the nebulosity by averted vision.

Try the faint planetary nebula NGC 2371/2 as a challenge object for 4- to 6-inch telescopes. This object's ghostly disk lies 4° southwest of the bright star Castor in Gemini. The faint glow of this nebula appears twin-lobed, making it a miniature version of the Little Dumbbell Nebula in Perseus. The nebula's southern portion is brighter than the northern half, and this fact makes it relatively easy to spot under a very dark sky.

With an 8- to 10-inch scope, try going after the weird galaxy NGC 1924 in Orion. This 12th-magnitude smudge lies a mere 2° west of the Orion Nebula (one of the most-observed little areas of the sky), yet few observers know about it. "Although omitted from every modern observing handbook," wrote Harrington a number of years ago, "it is faintly visible through my 8-inch f/7 Newtonian under exceptional skies. Its tiny, oval disk measures about 2' by 1' across, with a faint stellar nucleus nestled within." This is one challenge object that relatively few observers have ever seen.

As a challenge object for 12- to 14-inch scopes, try going for one of the classics of all-time, the Horsehead Nebula. This small (6' by 4' across) leaf of dark nebulosity in the shape of a horse's head juts out in front of the thin, faint emission nebula IC 434, south of the bright star Alnitak (Zeta [ζ] Orionis), the easternmost star in Orion's belt. This most celebrated dark nebula in the entire sky is also notoriously difficult to see; reported by some observers using telescopes as small as 5 inches in aperture, it normally requires a dark sky and a much larger scope, such as a 12-incher, to spot. Having logged thousands of hours of observing with many different telescopes, I've seen the Horsehead distinctly on only a small number of occasions, with a large scope under a very good sky. If you spot it, consider yourself inducted into a select club of skywatchers. Please e-mail us your observations of these deep-sky objects (and others), your photos, and copies of sketches you make, and we'll include them as we can on our web site and in the magazine.

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